
Good question. I'm gonna take that as a comment... for now.
Who is Salt? Apparently, it's Angelina Jolie acting as a female Russian spy named Evelyn Salt. And she's like a double double double agent or something. (I dunno, I haven't watched the movie yet :S)
Anyways, there's all this hype about not knowing who this Salt is. If you think about it, it's a pretty neat way of advertising - just keeping to the same 'theme line' and sticking it on radio ads, tv ads, pre-movie ads, bus ads, bus stop ads, billboard ads, newspaper ads etc. It's everywhere!
Even MSN is subliminaling messaging the movie, 'Salt'. Here's some examples:
- Traitor, Hero, Fugitave... Who is Salt?
- Click here to learn WHO IS SALT?
- Angelina Jolie stars in SALT. But who is salt?
- Can't make it on election day, Saturday 21st August? Vote earl- oh wait
Have some posters:

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Until I find out Who is Salt?,
I am Optimus Prime (aka mattlam), and i send this message to any surviving Autobots taking refuge among the stars. We are here. We are waiting. Autobots, roll out!
P.S. you can use it in your everyday friends vocab as a 'joke around' phrase!